This invention relates to digital communications systems and in particular to systems embodying asyncnronous transfer mode (ATM) technology.
The asynchronous transfer mode (ATM) technology is a flexible form of transmission which allows any type of service traffic, voice, video or data, to be multiplexed together on to a common means of transmission. In order for this to be realised, the service traffic must first be adapted typically into 53 byte cells comprising 5 byte headers and 48 byte payloads such that the original traffic can be reconstituted at the far end of an ATM network. This form of adaptation is performed in the ATM adaptation layer (AAL).
A recent development has been the introduction of the AAL-2 adaptation layer. This adaptation layer has been optimised to accommodate the demands of low bit-rate communications representing the increasing trend to greater voice compression. The adaptation layer is a multiplex of users in a single ATM connection where each user""s information is carried in short packets or minicells each with a header identifying the user channel and incorporating ancillary control information. This constitutes a dynamic trunk group of users in a single connection.
As telecommunications networks increase in complexity and carry increasing volumes of traffic, the current procedures for setting up connections between subscribers are limiting the performance of these networks. In particular, congestion may be caused by attempting to connect to a subscriber who is already busy, or by attempting to choose a route through an already congested part of the network. Thus equipment and resources can be wasted in attempts to set up calls which cannot be completed. A further problem is that of scalability. As the network expands to accommodate increased traffic and a larger number of subscribers, there is an increasing need to facilitate integration of new equipment into an existing network without simply increasing the congestion problem. Moreover, careful planning is required to ensure that calls can be routed through the network. This requires an ad-hoc distributed routing decision policy which limits the flexibility of the routing process as the call routing must be co-located with the switching node fabric.
An adaptation layer switching network is described by O. Kure et al. in Proceedings of the IFIP TC6 International Conference on Information Networks and Data Communication, Funchal, Madeira Island, Portugal, Apr. 18-21 1994. A method of switching synchronous transfer mode cells in a circuit emulated ATM switch using a layered protocol model is described in specification No. WO95/34977.
Reference is here directed to our co-pending application (Reference S D Brueckheimer 19) of even date and which relates to the application of PNNI signalling to control an ATM adaptation layer switching network.
According to one aspect of the invention there is provided an adaptation layer switching network in which functional partitioning provides a separation between service specific sublayers (SSCS), common part sublayers (CPS) and transport convergence whereby to support a range of SSCS functions via a common set CPS blocks.
According to another aspect of the invention there is provided method of functional partitioning of an adaptation layer switching network by providing a separation between service specific sublayers (SSCS), common part sublayers (CPS) and transport convergence whereby to support a range of SSCS functions via a common set CPS blocks.
According to a further aspect of the invention there is provided a telecommunications network comprising edge device nodes and adaptation layer switching nodes, wherein the edge nodes terminate the adaptation layer switching nodes to service access points, and wherein the adaptation layer switching nodes provide minicell switching points within the network.
The network architecture for adaptation layer switching is derived from AAL-2 technology. An adaptation layer switching network provides the capability to deliver a fully scalable network and nodal solutions that can utilise existing ATM infrastructure for transport. The use of AAL-2 technology and adaptation layer switching provides a network infrastructure suitable for carrying all delay sensitive and real-time services with a GoS (grade of service) that meets ITU standards for delay and distortion. The network can be constructed from two basic building blocks. These comprise edge devices and adaptation layer switches.
The arrangement and method exploit the ATM adaptation layer (AAL-2) to configure networks and switching functions. In particular, the AAL-2 adaptation switching function is employed to provide the ability to establish and control an AAL-2 minicell connection across many nodes thus forming an adaptation layer switching network. The network can readily be scaled to global proportions.
The arrangement and method also provide a functional partitioning of AAL-2 to realise the necessary functions for a switching network. These functions include a service specific convergence function (SSCF) and a minicell switching/relay function. The partitioning achieves a clear separation between the SSCS, CPS and transmission convergence (TC) sublayers, and enables a common CPS to support a multiplicity of SSCS functions and a full range of transmission media.